For many years, petroleum has been recovered from subterranean reservoirs through the use of drilled wells and production equipment. During the production of desirable hydrocarbons, such as crude oil and natural gas, a number of other naturally occurring substances may also be encountered within the subterranean environment.
Although supercritical carbon dioxide (CO2) flooding is a widely used method in tertiary oil recovery, the method presents many challenges, such as inefficient gas utilization, poor sweep efficiency and low oil recovery due to viscous fingering and gravity segregation. One recent development is the application of CO2 foam in order to reduce the CO2 mobility, especially in high permeability zones of the reservoir. In the past, CO2 foam has been produced using surfactant mixtures prepared through the combination of betaines and alpha-olefin sulfonates (AOS). The efficiency of these prior art CO2 foam efforts often decreases sharply during flooding as a result of contact with crude oil, retention of surfactants on the geologic formation, high salinity in formation water, a lack of reservoir pressure necessary to keep the CO2 as a supercritical fluid and high reservoir temperatures.
There is, therefore, a need for the development of inventive surfactant formulations which have better tolerance to these factors. It is to these and other objectives that the present invention is directed.